The invention relates to medical devices suitable for contacting a patient's bodily fluids, including a substrate with a polymer material covering at least a portion of the substrate.
A variety of medical devices are designed particularly for contact with a patient's bodily fluids. The duration of this contact may be relatively short, as is typical with surgical instruments, or may be long term, as is typical with prosthetic heart valves implanted into the body of a recipient, and other implanted prostheses. Some articles such as catheters can have either short term or relatively long term contact.
Prostheses, i.e., prosthetic articles, are used to repair or replace damaged or diseased organs, tissues and other structures in humans and animals. Prostheses generally must be biocompatible since they are typically implanted for extended periods of time. Physicians use a variety of prostheses to correct problems associated with the cardiovascular system, especially the heart. For example, the ability to replace or repair diseased heart valves with prosthetic devices has provided surgeons with a method of treating heart valve deficiencies due to disease and congenital defects. A typical procedure involves removal of the native valve and surgical replacement with a mechanical or bioprosthetic, i.e., tissue based, valve. Another technique uses an annuloplasty ring to provide structural support to the natural annulus of the native valve.
Many biocompatible medical devices and/or their components have specific requirements with respect to their mechanical and physical properties. For example, the medical devices are often limited in their size while needing fairly complex structural features. At the same time, the devices and/or their components may be subjected to demanding mechanical requirements, such as mechanical strength and long term wear requirements. Thus, there are significant restraints imposed on the design of many medical devices and/or their components.
As a particular example, heart valve stents are used to support leaflet components within a bioprosthetic heart valve. Heart valve stents have been produced from polymers, such as polyacetals, for example Delrin® and Celcon®, or metals, such as titanium or a cobalt-chromium-nickel alloy, for example, Elgiloy® Polymer heart valve stents have been known to fail due to fatigue and creep. Furthermore, polymer heart valve stents need to be relatively bulky in order to withstand the repeated loading over the lifetime of the prosthetic valve.
In contrast, heart valve stents made from spring metals, such as Elgiloy®, exhibit better mechanical properties, such as strength and fatigue endurance, and can have a smaller cross-section than corresponding polymer stents. Metal heart valve stents, however, generally must be kept quite simple in geometry, and typically consist of a simple wire form. As the geometry of the metal stent becomes more complex, the stent generally includes more metal joints, which can weaken the structure. Also, metal stents may require welding or crimping during their manufacture which can weaken the stent. Similar observations regarding properties and construction of heart valve stents can also apply to other medical devices and their components.